1. Field of the Invention
The present invention relates to a plasma display panel suitably used for a flat display panel, a manufacturing method thereof, and a plasma display. The present invention more specifically relates to a plasma display panel with improved contrast, a manufacturing method thereof, and a plasma display.
2. Description of the Related Art
There are two kinds of plasma display panels (PDPs), AC type and DC type PDPs. The AC type PDP has electrodes covered with dielectric because of the operating method and is indirectly operated in an AC discharge state. The DC type PDP has electrodes exposed in a discharge space and is operated in a DC discharge state. The AC type plasma displays are divided based on the driving method into a memory operation type using display cell memories, and a refresh operation type that does not use memories. Note that the luminance by the plasma display is in proportion with the number of discharge. The refresh type display whose luminance is reduced for an increased display capacity is mainly used for a plasma display with a small display capacity.
FIG. 1 is a perspective view of a single display cell in an AC type plasma display panel. FIGS. 2A and 2B are a plan view and a sectional view, respectively showing in detail the shapes of a scan electrode and a common electrode in a conventional plasma display panel.
A display cell is provided with two insulating glass substrates 101 and 102. The insulating substrate 101 is to be a back panel substrate, while the insulating substrate 102 is to be a front panel substrate.
Transparent electrodes 103 and 104 are provided on the surface of the insulating substrate 102 facing the insulating substrate 101. The transparent electrodes 103 and 104 extend in the horizontal direction of the panel (in the horizontal direction). Bus electrodes 105 and 106 are provided to overlap the transparent electrode 103 and the common electrode 104, respectively. The bus electrodes 105 and 106 are each for example a thin film electrode of CrCu or Cr having a thickness from 1 xcexcm to 4 xcexcm. The bus electrodes are provided to reduce the electrode resistance values between the electrodes and externally provided drives. The transparent electrode 103 and the bus electrode 105 form a scan electrode 115, while the transparent electrode 104 and the bus electrode 106 form a common electrode 116. Within one display cell, the bus electrodes 105 and 106 are provided in the furthermost positions from the surface discharge gap between the transparent electrodes 103 and 104. There are a dielectric layer 112 to cover the transparent electrodes 103 and 104 and a protection layer 114 of magnesium oxide or the like to protect the dielectric layer 112 against discharge.
There is a data electrode 107 perpendicular to the scan electrode 103 and the common electrode 104 on the surface of the insulating substrate 101 facing the insulating substrate 102. The data electrode 107 therefore extends in the vertical direction of the panel (the vertical direction). There are barrier ribs 109 to divide display cells in the vertical direction. A dielectric layer 113 to cover the data electrode 107 is provided. A phosphor layer 111 to convert a ultraviolet beam generated by gas discharge into a visible light beam 110 is formed on the side of the barrier rib 109 and the surface of the dielectric layer 113. A discharge gas space 108 is secured by the barrier ribs 109 in the space between the insulating substrates 101 and 102. Then, a helium, neon, or xenon gas, or a mixture gas thereof as a discharge gas is filled in the discharge gas space 108.
In the plasma display panel as described above, when the potential difference between the scan electrode 115 and the common electrode 116 is above a prescribed value, discharge is generated, and light emission 110 is caused accordingly.
Writing selective type driving operation in the conventional plasma display panel as described above will now be described. FIG. 3 is a timing chart for use in illustration of the writing selective type driving operation in the conventional plasma display panel. Each sub field consists of four periods, a priming period, an address period, a sustaining period, and a charge erasure period. These four periods are sequentially set.
In the priming period, a saw-toothed priming pulse Ppr-s is applied to the scan electrode, and a rectangular waveform priming pulse Ppr-c is applied to the common electrode. The priming pulse Ppr-s is a pulse of the positive polarity, while the priming pulse Ppr-c is a pulse of the negative polarity. According to The Technical Report of The Proceeding of The Institute of Electronics, Information and Communication Engineers, vol. EID 98-95, p. 91, January 1991, the use of voltage in a ramp voltage waveform at 7.5 V/xcexcsec or less can lower the black luminance. The smaller the gradient of the voltage, the lower is the black luminance, while at too small a gradient the time period for the voltage to reach the necessary level for priming discharge is prolonged, which prolongs the priming period. Then, the sustaining period must be shortened, and the peak luminance is lowered in the sustaining discharge, which lowers the contrast. Therefore, a voltage gradient of about 4 V/xcexcsec is typically used.
In response to the applied priming pulses Ppr-s and Ppr-c, priming discharge is generated in a discharge space in the vicinity of the gap between the scan electrode and the common electrode. Active particles which make easier the following sustaining discharge in the cell are generated, while wall charge of the negative polarity is attached on the scan electrode and wall charge of the positive polarity is attached on the common electrode. Then, a charge control pulse Ppe-s is applied to the scan electrode. This causes weak discharge to take place, so that the wall charge of the negative polarity on the scan electrode and the wall charge of the positive polarity on the common electrode are reduced.
In the following address period, a display cell for light emission is selected, and writing discharge is generated only at a cell selected by a scan pulse Psc-s of the negative polarity applied to the scan electrode and a data pulse Pd of the positive polarity applied to a data electrode. Wall charge is attached to the electrode of the cell to emit light in the following sustaining period. When writing discharge is generated, wall charge is attached to the discharge cell. In contrast, discharge cells without writing discharge remain with little wall charge after the charge erasure.
In the following sustaining period, light emission is caused for display, a pulse starts to be applied from the common electrode side, and then sustaining pulses Psus-s and Psus-c of the negative polarity are alternately applied to the scan electrode and the common electrode, respectively. At the time, since there is extremely little wall charge at the discharge cells without writing during the address period, sustaining discharge is not generated when a sustaining pulse is applied to the discharge cells.
Meanwhile, in the discharge cell with writing discharge during the address period, the scan electrode is attached with positive charge, while the common electrode is attached with negative charge. Therefore, the sustaining pulse voltage of the negative polarity to the common electrode and the wall charge voltage are superposed on each other, the voltage across the region between the electrodes exceeds the threshold voltage for discharge, and intensified discharge is generated (hereinafter referred to as xe2x80x9cstrong dischargexe2x80x9d).
Once discharge is generated, wall discharge is provided to cancel voltage being applied to each electrode. Therefore, the negative charge is attached to the common electrode, while the positive charge is attached to the scan electrode. For the following sustaining pulse, the scan electrode side has a positive voltage pulse, and therefore effective voltage superposed with the wall charge and applied to the discharge space exceeds the threshold voltage for discharge to generate discharge. Thereafter, the same process is repeated to sustain discharge. The luminance is determined based on how many times the discharge is repeated.
In the following charge erasure period, a sustaining erasure pulse Pse-s of the negative polarity is applied to a scan electrode Si. The sustaining erasure pulse Pse-s of the negative polarity is a pulse in a saw-toothed waveform. Thus, the wall charge attached to each electrode when the previous sub field has light emission is erased. Meanwhile, the state of all the discharge cells in the panel can be equalized regardless of the presence/absence of light emission in the previous sub field.
Japanese Patent Laid-Open Publication No. Hei. 11-67100 discloses a plasma display panel including a stripe-shaped barrier rib structure. According to the disclosure, bus electrodes on the scan electrode side are positioned on the discharge gap side for reducing the power consumption.
Japanese Patent Laid-Open Publication No. 2000-243299 discloses a plasma display panel directed to prevention of discharge interference between adjacent display cells. According to the disclosure, a comb-toothed transparent electrode is provided while bus electrodes are provided on the discharge gap side.
In the conventional plasma display panels, however, the luminance when weak discharge is generated in a priming period i.e., so-called black luminance is high, and therefore sufficient contrast is not provided. FIG. 4A is a timing chart for use in illustration of the relation between the potential difference between surface discharge electrodes and the discharge intensity in a sustaining period, while FIG. 4B shows the relation in a priming period. Note that the potential difference in FIG. 4A is provided by application of one sustaining pulse. As shown in FIGS. 4A and 4B, the intensity of discharge in the sustaining period, in other words, the intensity of the sustaining discharge is extremely larger than the intensity of discharge in the priming period, in other words the intensity of the priming discharge. The contrast is represented by the ratio of the peak luminance in the sustaining period relative to the black luminance, and is substantially equal to the ratio of the intensity of the sustaining discharge relative to the intensity of the priming discharge. Therefore, the larger the light emission by the priming discharge, the lower is the contrast.
Also in the plasma display panel disclosed by Japanese Patent Laid-Open Publication No. Hei. 11-67100, the expansion of the priming discharge is large, and the black luminance is not sufficiently low. In addition, the scan electrode and common electrode are not symmetrical, and therefore the positional relation between the scan electrode and the common electrode must be constant among the display cells. This is because when for example the scan electrode and common electrode are inverted between adjacent display lines in order to narrow the non-discharge gap, the picture quality degrades with moirxc3xa9 or the like.
In the plasma display panel disclosed by Japanese Patent Laid-Open No. 2000-243299, the sustaining discharge does not spread over the entire display cell in order to prevent the interference between the display cells.
It is an object of the present invention to provide a plasma display panel which allows a high contrast to be obtained and preferably the sustaining voltage and threshold voltage for discharge to be reduced, so that the power consumption can be reduced, a manufacturing method thereof, and a plasma display.
The plasma display panel according to the present invention includes first and second substrates placed opposed to each other, a plurality of scan electrodes and common electrodes provided on the surface side of the first substrate facing the second substrate and extending in a first direction, and a plurality of data electrodes provided on the surface side of the second substrate facing the first substrate and extending in a second direction orthogonal to the first direction, a display cell is provided each at the crossing point of the scan electrode and common electrode and the data electrode, and driving voltage increased with time such as ramp voltage having a voltage gradient of at most 7.5 V/xcexcsec is applied to the scan electrode in a priming period. In the plasma display panel, the scan electrode and the common electrode include a transparent electrode, and a bus electrode formed more on the side of a discharge gap on the transparent electrode than the center thereof, extending in the first direction and shielding light emitted in the display cell by the applied driving voltage.
Note that the transparent electrode is preferably shared between display cells arranged in the first direction so that the electrode area is maximized to increase the peak luminance. Meanwhile, the transparent electrode may separately be provided for each display cell and have a comb-tooth shape when viewed two-dimensionally. Note however that when the transparent electrode is formed in a comb-tooth shape, preferably a mesh barrier rib structure is provided on the second substrate or the thickness of the bus electrode is at least 5 xcexcm. The transparent electrode may have an opening formed for each display cell. In this case, the opening is preferably formed in contact with the bus electrode when viewed two-dimensionally. Note however that the transparent electrode may be without an opening.
Another plasma display panel according to the present invention includes first and second substrates placed opposed to each other, a plurality of scan electrodes and common electrodes provided on the surface side of the first substrate facing the second substrate and extending in a first direction, and a plurality of data electrodes provided on the surface side of the second substrate facing the first substrate and extending in a second direction orthogonal to the first direction, a display cell is provided each at the crossing point of the scan electrode and common electrode and the data electrode, and driving voltage increased with time such as ramp voltage having a voltage gradient of at most 7.5 V/xcexcsec is applied to the scan electrode in a priming period. In the plasma display panel, the scan electrode and common electrode include a transparent electrode and a bus electrode formed on the transparent electrode and extending in the first direction, the transparent electrode includes a base portion, and a projection jutting out from the base portion to another transparent electrode within the same display cell.
According to the present invention, the area of the projection when viewed two-dimensionally is preferably in the range from 10% to 50% of the value produced by Wxc3x97H, where W represents the width of the cell, and H represents the distance between the top of the projection and the base portion.
The length of the side end of the projection forming the shortest discharge gap is preferably substantially equal to the length of the side end of the projection in contact with the base portion. In other words, the projection preferably has a rectangular shape.
Another plasma display panel according to the present invention includes first and second substrates placed opposed to each other, a plurality of scan electrodes and common electrodes provided on the surface side of the first substrate facing the second substrate and extending in a first direction, a plurality of data electrodes provided on the surface side of the second substrate facing the first substrate and extending in a second direction orthogonal to the first direction, a display cell is provided each at the crossing point of the scan electrode and common electrode and the data electrode, driving voltage increased with time such as ramp voltage having a voltage gradient of at most 7.5 V/xcexcsec is applied to the scan electrode in a priming period. In the plasma display panel, the scan electrode and common electrode include a bus electrode formed on the transparent electrode and extending in the first direction and an island-shaped electrode formed more on the discharge gap side on the transparent electrode than the center thereof.
According to the present invention, the island-shaped electrode preferably has an area smaller than that of the bus electrode. Therefore, the island-shaped electrode may be thinner than the bus electrode, or does not have to be continuous in the first direction.
According to the present invention, the island-shaped electrode may be made of the same material as that of the bus electrode, and preferably has a thickness of at least 5 xcexcm. The island-shaped electrode is preferably made of one selected from the group consisting of an indium tin oxide film, a NESA film, a Cr film and a Cu film and preferably faces the discharge gap. The island-shaped electrode may face the discharge gap.
The bus electrode preferably has a thickness of at least 5 xcexcm. Note that the bus electrode may have a black first electrode formed on the transparent electrode, and a second electrode formed on the first electrode and containing Ag.
Another plasma display panel according to the present invention includes first and second substrates placed opposed to each other, a plurality of scan electrodes and common electrodes provided on the surface side of the first substrate facing the second substrate and extending in a first direction, and a plurality of data electrodes provided on the surface side of the second substrate facing the first substrate and extending in a second direction orthogonal to the first direction, a display cell is provided each at the crossing point of the scan electrode and common electrode and the data electrode, driving voltage increased with time such as ramp voltage having a voltage gradient of at most 7.5 V/xcexcsec is applied to the scan electrode in a priming period. In the plasma display panel, the scan electrode and common electrode include a transparent electrode and a bus electrode formed on the transparent electrode and extending in the first direction. The transparent electrode has an opening having its end on the non-discharge gap side located in a position apart from its end on the discharge gap side by 1 to 1.5 times as large as the discharge gap.
Another plasma display panel according to the present invention includes first and second substrates placed opposed to each other, a plurality of scan electrodes and common electrodes provided on the surface side of the first substrate facing the second substrate and extending in a first direction, and a plurality of data electrodes provided on the surface side of the second substrate facing the first substrate and extending in a second direction orthogonal to the first direction, a display cell is provided each at the crossing point of the scan electrode and common electrode and the data electrode, and driving voltage increased with time such as ramp voltage having a voltage gradient of at most 7.5 V/xcexcsec is applied to the scan electrode in a priming period. In the plasma display panel, the scan electrode and common electrode include a transparent electrode, a first bus electrode formed on the transparent electrode more on the non-discharge gap side than the center thereof and a second bus electrode formed on the transparent electrode more on the discharge gap side than the center thereof, extending in the first direction and shielding light generated in the display cell by the applied driving voltage. The second bus electrode is thinner than the first bus electrode.
The second bus electrode may be disconnected in the first direction.
In a sustaining period, sustaining pulses in phase may be applied to one of the scan electrode and common electrode between adjacent display cells in the second direction, and interlace display may be provided. The relative positional relation between the scan electrode and the common electrode may be reversed between adjacent cells in the second direction.
There is preferably a mesh barrier rib structure formed on the second substrate for separating the display cells. In the scan electrode and the sustain electrode, a region at least 10 xcexcm apart from the side end of the scan electrode and sustain electrode facing the discharge gap is preferably made of one selected from the group consisting of an indium tin oxide film, a NESA film, a Cr film, and a Cu film.
According to the present invention, the priming discharge is localized in the vicinity of the discharge gap, and there is no light emission in the periphery of the display cell. Meanwhile, light emission by sustaining discharge is generated in the entire display cell. Therefore, the black luminance is lowered, and the luminance in the sustaining discharge improves, which improves the contrast.
The plasma display according to the present invention includes any one of plasma display panels described above.
By a method of manufacturing a plasma display panel according to the present invention, a plasma display panel having a island-shaped electrode made of the same material as the bus electrode is produced. The method includes the steps of forming the transparent electrode on the second substrate, forming a material film for the bus electrode and an island-shaped electrode on the transparent electrode, and patterning the material film, thereby forming the bus electrode and the island-shaped electrode at a time.